Determining a website's 'root' location - php

Question

I need some help with concepts and terminology regarding website 'root' urls and directories.
Is it possible to determine a website's root, or is that an arbitrary idea, and only the actual server's root can be established?
Let's say I'm writing a PHP plugin that that will be used by different websites in different locations, but needs to determine what the website's base directory is. Using PHP, I will always be able to determine the DOCUMENT_ROOT and SERVER_NAME, that is, the absolute URL and absolute directory path of the server (or virtual server). But I can't know if the website itself is 'installed' at the root directory or in a sub directory. If the website was in a subdirectory, I would need the user to explicitly set an "sub-path" variable. Correct?

Answer 1

Answer to question 1: Yes you need a variable which explicitly sets the root path of the website. It can be done with an htaccess file at the root of each website containing the following line :
SetEnv APP_ROOT_PATH /path/to/app
http://httpd.apache.org/docs/2.0/mod/mod_env.html
And you can access it anywhere in your php script by using :
<?php $appRootPath = getenv('APP_ROOT_PATH'); ?>
http://php.net/manual/en/function.getenv.php

Answer 2

Will $url and $dir always be pointing to the same place?
Yes
<?php
$some_relative_path = "hello";
$server_url = $_SERVER["SERVER_NAME"];
$doc_root = $_SERVER["DOCUMENT_ROOT"];
echo $url = $server_url.'/'. $some_relative_path."<br />";
echo $dir = $doc_root.'/'. $some_relative_path;
Output:
sandbox.phpcode.eu/hello
/data/sandbox//hello

Answer 3

You shouldn't need to ask the user to provide any info.
This snippet will let your code know whether it is running in the root or not:
<?php
// Load the absolute server path to the directory the script is running in
$fileDir = dirname(__FILE__);
// Make sure we end with a slash
if (substr($fileDir, -1) != '/') {
$fileDir .= '/';
}
// Load the absolute server path to the document root
$docRoot = $_SERVER['DOCUMENT_ROOT'];
// Make sure we end with a slash
if (substr($docRoot, -1) != '/') {
$docRoot .= '/';
}
// Remove docRoot string from fileDir string as subPath string
$subPath = preg_replace('~' . $docRoot . '~i', '', $fileDir);
// Add a slash to the beginning of subPath string
$subPath = '/' . $subPath;
// Test subPath string to determine if we are in the web root or not
if ($subPath == '/') {
// if subPath = single slash, docRoot and fileDir strings were the same
echo "We are running in the web foot folder of http://" . $_SERVER['SERVER_NAME'];
} else {
// Anyting else means the file is running in a subdirectory
echo "We are running in the '" . $subPath . "' subdirectory of http://" . $_SERVER['SERVER_NAME'];
}
?>

Answer 4

I have just had the same problem. I wanted to reference links and other files from the root directory of my website structure.
I tried the following but it would never work how I wanted it:
$root = $_SERVER['DOCUMENT_ROOT'];
echo "Link";
echo "Link";
But the obvious solution was just to use the following:
echo "Link";
echo "Link";